A composite refers to a material consisting of two or more individual constituents. A reinforcing constituent is embedded in a matrix to form the composite. Common composites are composed of glass or carbon fiber in a plastic resin. Natural fibers can also be used. Resins can be of the form of thermoset or thermoplastic materials which each have their own unique properties. Epoxy resins are traditionally used for fiber reinforced composites. However, the epoxy resins require the use of a curing agent. Polyamines can be mentioned as examples of such curing agents for epoxy resins. Commonly used compounds are diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), ethyleneamine etc. There is, however, a need for more sustainable and bio-based curing agents that can be used to replace conventional polyamine curing agents. Prior art recognizes the use of lignin as binder or filler agent mixed with epoxy resin in composites. However, in these composites a conventional polyamine curing agent is required.
The inventors have, however, recognized the need for a method, which would result in a higher replacement level of e.g. petroleum based materials in resin matrixes and thus in a more environmentally friendly fiber reinforced composite.